Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F10/00—Homopolymers and copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond

Definitions

• the present invention relates to catalysts for the polymerization of olefins in the form of a suspension or emulsion, the procedure for their production and their use in the polymerization of olefins.
• Ziegler-Natta type catalysts are already known in the art, which are active in the polymerization of ⁇ -olefins, generally formed by the combination of an organometallic compound of the elements belonging to groups I to III and a compound of a transition metal belonging to groups IV to VI of the Periodic Table (Boor Jr., "Ziegler-Natta Catalysts and Polymerization", Academic, New York, 1979).
• an aluminium alkyl is used as the organometallic compound and a titanium halide as the transition metal.
• the possibility of binding or depositing the titanium halide on a solid and granular support is also known (Karol F.J., Catal. Rev. - Sci. Eng., 26 , 384, 557-595, 1984).
• the first aspect of the present invention relates to a procedure for the preparation of a catalyst for the polymerization of olefins containing magnesium, chlorine, aluminium and at least one transition metal, said catalyst being in a dispersed or emulsion form in an inert diluent, which includes:
• the magnesium dialkyls which can be used in step (i) of the procedure are compounds which can be defined with the formula MgR'R'', where R' and R'', the same or different, each independently represents an alkyl group, linear or branched, containing 1 to 10 carbon atoms.
• Specific examples of magnesium dialkyl are: magnesium diethyl, magnesium ethyl butyl, magnesium dihexyl, magnesium butyl octyl, and magnesium dioctyl.
• the corresponding halides, for example chlorides, of magnesium alkyl may also be used.
• Suitable diluents for the purpose are organic diluents, liquid under the operating conditions, and inert towards the reagents magnesium dialkyl and aluminium chloride and may be conveniently selected from aliphatic hydrocarbons and silicon oils.
• step (i) of the procedure a dispersion is obtained containing magnesium chloride which is solid and crystalline with regular particles, having a diameter ranging from several microns to 1 mm, depending on the concentration of the reagents, the geometrical form of the reactor, the viscosity of the dispersing medium and, more generally, on the fluodynamics of the system.
• magnesium dialkyl and aluminium trichloride When the contact between magnesium dialkyl and aluminium trichloride is carried out at a temperature higher than 105°C, and generally from 110 to 150°C, and for a period of about 0.5 to about 3 hours, a complete and irreversible change in the physical state of the mixture is obtained which from an increasingly dispersed suspension reaches the limit of a state of emulsion of extremely fine drops with microscopic dimensions in the diluent used.
• the stability of this emulsion does not depend at all on the stirring of the system, the temperature at which is kept (at least until -20°C) and how long it is kept before use.
• the dispersion or emulsion thus obtained are used as precursors for the preparation of catalysts which are active in the polymerization of olefins.
• the dispersion or emulsion is put in contact and reacted with at least one compound of a transition metal,normally selected from halides, especially chlorides, alkoxides, especially C2-C4 alkoxides, and halogenalkoxides, especially the chloroalkoxides of titanium, zirconium, hafnium and vanadium.
• halides especially chlorides, alkoxides, especially C2-C4 alkoxides, and halogenalkoxides, especially the chloroalkoxides of titanium, zirconium, hafnium and vanadium.
• halides especially chlorides, alkoxides, especially C2-C4 alkoxides
• halogenalkoxides especially the chloroalkoxides of titanium, zirconium, hafnium and vana
• the reaction between the dispersion or emulsion and the compound of a transition metal is normally carried out with an atomic ratio between magnesium and transition metal generally ranging from 30:1 to 0.5:1 and preferably in the range of 20:1-25:1.
• the reaction is carried out at a temperature ranging from 50 to 120°C, and preferably in the range of 60-90°C, and for a period of 0.5 to 4 hours, and preferably for 1-2 hours, to obtain a catalyst in a disperse or emulsion form, depending on the kind of precursor used.
• the catalysts thus obtained generally contain magnesium, transition metal, aluminium and chlorine in atomic proportions of 4-25:1:10-50:40-150.
• the solid can be separated from the diluent at the end of step (ii).
• the catalytic dispersions and emulsions are used directly in the polymerization procedure where they have advantages deriving from their physical form which enables them to be fed with liquid pumps, consequently simplifying plant equipment.
• step (ii) of the procedure is carried out in the presence of a Lewis base (or internal electron donor).
• This Lewis base may be selected from ethers, amines, esters, alcoholates, silanic compounds, ketones and phosphoramides.
• the catalysts of the present invention are used in procedures for the (co)polymerization of alpha-olefins combined with a co-catalyst normally selected from aluminium trialkyls and halides (especially chlorides) of aluminium alkyl, containing from 1 to 6 carbon atoms in the alkyl portion.
• aluminium trialkyls such as aluminium triethyl, aluminium tributyl, aluminium triisobutyl and aluminium trihexyl are preferred.
• the atomic ratio between the aluminium (in the co-catalyst) and titanium (in the catalyst) generally ranges from 0.5:1 to 1.000:1 and preferably from 50:1 to 200:1.
• the co-catalyst may be complexed with an electron donor compound, such as a silane alkoxy like dimethoxy diphenyl silane.
• the catalysts of the present invention can be used in the production of polymers and copolymers of ethylene, propylene, butene-1, 4-methyl-1-pentene and hexene-1, in procedures carried out in suspension in an inert diluent, in solution, or in procedures carried out at a high temperature and pressure in tubular or vessel reactors.
• the stirred suspension is gradually heated in about 1 hour to 90°C, and is left at this temperature for 1 hour. A morphological variation is observed in the suspension, with the appearance of a grey crystalline solid.
• This solid which is composed of magnesium chloride in the form of solid and regular microcrystals with an average diameter of 10 ⁇ m, is used in suspension in n-heptane for the preparation of the catalyst in the following examples.
• the solid obtained from this treatment is repeatedly washed with n-heptane at 90°C, until the titanium has completely disappeared from the washing liquid.
• the following products are charged, in this order, into a stirred 5 litre reactor: 1.900 ml of anhydrous n-hexane, 0.5 g of aluminium triethyl as co-catalyst and 0.07 g of the catalyst prepared in Example 2.
• the atomic ratio between the aluminium in the co-catalyst and the titanium in the catalyst is thus equal to 200/1.
• the reactor is brought to a temperature of 85°C, is pressurized with hydrogen up to 5 atm and ethylene is then fed up to 9 atm (molar ratio hydrogen/ethylene equal to 1/1). The pressure is kept in the following two hours with the feeding of ethylene.
• the polymerization is interrupted by charging 20 ml of a 10% by weight alcohol solution of ionol (2,6-di-t-butyl-p-cresol) into the reactor.
• Example 4 The same procedure is used as described in Example 4, using 1.0 g of aluminium triethyl as co-catalyst and 0.21 g of the catalyst prepared in Example 3.
• the atomic ratio between the aluminium in the co-catalyst and the titanium in the catalyst is thus equal to 100/1.
• 1.224 g of polyethylene are obtained with a productivity of 5.8 k, expressed as kg of polyethylene per gram of catalyst and a yield of 416 kg, expressed as kg of polyethylene per gram of titanium in the catalyst.
• the following products are charged, in this order, into a 5 litre stirred reactor: 1.900 ml of anhydrous n-hexane, 0.5 g of aluminium triethyl as co-catalyst and 1.5 ml of the emulsion obtained in Example 7, containing 0.04 mmoles of titanium.
• the atomic ratio between the aluminium in the co-catalyst and the titanium in the suspension is thus equal to 100/1.
• the reactor is brought to a temperature of 85°C, is pressurized with hydrogen up to 5 atm and ethylene is then fed up to 9 atm (molar ratio hydrogen/ethylene equal to 1/1). The pressure is maintained for a further two hours feeding ethylene.
• a sample of the catalytic emulsion obtained in Example 7 is used in an ethylene/butene copolymerization test at high pressure in a vessel reactor, using aluminium triethyl as co-catalyst, with an atomic ratio Al:Ti of 10:1.
• test conditions are:
• the following products are charged, in this order, into a 5 litre stirred reactor: 1.900 ml of anhydrous n-hexane, 0.25 g of aluminium triethyl as co-catalyst and 2.0 ml of the emulsion obtained in Example 10, containing 0.02 mmoles of titanium.
• the atomic ratio between the aluminium in the co-catalyst and the titanium in the suspension is thus equal to 100/1.
• the reactor is brought to a temperature of 85°C, is pressurized with hydrogen up to 5 atm and ethylene is then fed up to 9 atm (molar ratio hydrogen/ethylene equal to 1/1). The pressure is maintained for the following two hours feeding ethylene.
• the following products are charged, in this order, into a 5 litre stirred reactor: 1.900 ml of anhydrous n-hexane, 0.5 g of aluminium triethyl as co-catalyst and 1.2 ml of the emulsion obtained in Example 11, containing 0.04 mmoles of titanium.
• the atomic ratio between the aluminium in the co-catalyst and the titanium in the suspension is thus equal to 100/1.
• the reactor is brought to a temperature of 85°C, is pressurized with hydrogen up to 5 atm and ethylene is then fed up to 9 atm (molar ratio hydrogen/ethylene equal to 1/1). The pressure is maintained for the following two hours by feeding ethylene.

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• 1991
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